The invention relates to a method for protecting vehicles against unauthorized use by broadcasting a use enabling signal from a master station.
Such a protection arrangement is disclosed, for example, German patent document DE-A 44 40 975.3-51, in which an anti-theft control unit and a receiving device of a mobile communication system are arranged in the vehicle. A communication structure aboard the vehicle permits, on the one hand, the exchange of data between an anti-theft control unit and the receiving device and, on the other hand, the exchange of data between the anti-theft control unit and at least one operationally necessary control unit of the vehicle. As long as a vehicle has not been reported stolen, or provided another unauthorized use of the vehicle has not been determined, signals are transmitted from a master station to the vehicle via the mobile communication system at regular time intervals, the said signals being received by the receiving device. The reception of the signals is conveyed from the receiving device to the anti-theft control unit via the communication structure. The signals are detected and if they are determined to be directed at the vehicle, operation of the vehicle is enabled for a prescribed time period which is longer than the time interval between two successive signals. If no signal is received before expiration of the period for which operation of the vehicle is enabled, the enabling of operation of the vehicle is not prolonged. The anti-theft control unit then actuates the at least one operationally necessary control unit via the communication structure and prevents the further operation of this control unit, at least at the next attempt to activate the vehicle.
This measure prevents a vehicle from being used without authorization over a relatively long period of time. Also, operation is not dependent on signals which are emitted by the vehicle and may be disrupted, but is instead dependent exclusively on reception of the signals broadcast by the master station so that disruption or destruction of the communication system does not permit prolonged use of the vehicle.
A disadvantage of this method, however, is that it does not enable a location of the vehicle. As a result, it is still possible, for example after misappropriating the vehicle, to transfer it to another location on a transporter, without risk. In addition, a relatively long period of time may pass between the time when the unauthorized use of the vehicle starts and the time when the information relating to the unauthorized use is conveyed to the master station, so that broadcasting of the signals may not commence until a considerable period of time after the unauthorized use has started. During this period of time, the unauthorized use of the vehicle can be continued unhindered. In addition, if a large number of vehicles are to be protected in this manner, a very large transmission capacity is required for the signals which are broadcast at regular time intervals. Therefore, this method is suitable only for protecting a strictly limited number of vehicles.
Furthermore, it is known for example from the article "Satellitenhilfe gegen Auto-Klau" Using satellites to combat car theft! by R. Gramm in the journal Funkschau Issue 16/1993 pp. 42 to 45 to provide a locating system which is arranged in the vehicle and determines, continuously or at regular intervals, the geographic area the vehicle is located, and conveys this information to a master station via a transmitting device aboard the vehicle end. A receiving unit for receiving and evaluating the locating information broadcast by the transmitting device is present in this master station. The location of the vehicle can thus be monitored continuously or at regular intervals in the master station.
This device has the disadvantage that it provides no arrangement for disabling the vehicle. The tracking of the vehicle by the master station can also be prevented, for example, by destroying the transmitting device at the vehicle end or the locating system. In addition, a large capacity in terms of transmitting devices and transmitting frequencies must be made available if a large number of vehicles are to be tracked continuously. If for example a digital radio telephone is used as the mobile communication system, high communication costs are incurred in order continuously to convey the results of the locating of the vehicle to the master station.
The object of the present invention is to prevent reliably the unauthorized use of a vehicle, even if the communication between the vehicle and master station is prevented.
Another object of the invention is to locate the vehicle, at least if an unauthorized use occurs. In this context, the system is to operate in a cost effective way and is also to be capable of monitoring a large number of vehicles.
This object is achieved by the method according to invention, in which a master station broadcasts an enabling signal. For this purpose, an antitheft control unit located aboard the vehicle transmits a status signal containing vehicle identifying data when enabling of the vehicle is cancelled. The master station checks to determine whether it has received an indication of unauthorized use of the vehicle, and absent such an indication, transmits an enabling signal, which causes the antitheft control unit to extend the authorized use of the vehicle for a predetermined period. If no enabling signal is received within a prescribed time period, at least one operationally essential vehicle system is disabled, and a vehicle location signal is broadcasted from the vehicle.
Communication between the vehicle and master station is bidirectional. As a result, it is possible not only to transmit exclusively a position message of the vehicle to the master station or to transmit exclusively enabling signals to the vehicle from the master station, but also to make the communication appropriate to requirements. The necessary transmission of information is substantially reduced in that the enabling signal is not broadcast continuously, but only when requested by the vehicle. On the other hand, the master station is simultaneously informed of the current location of the vehicle at least if the vehicle is not enabled. The communication between the vehicle and the master station must be maintained so that the enabling signal can be transmitted from the master station to the vehicle in good time.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.